1. Field of the Invention
This invention relates to a hydraulic control mechanism for a brake system. A first master cylinder in response to an operator input supplies the hydraulic control mechanism with first and second hydraulic fluid pressure signals. When the first hydraulic fluid pressure signal is larger than or equal to the second hydraulic fluid pressure signal, the first hydraulic fluid pressure signal moves a plunger to operate a hydraulic booster, which in turn supplies an input to a second master cylinder to effect a brake application. When the first hydraulic fluid signal is smaller than the second hydraulic fluid signal, the second hydraulic fluid signal moves the plunger to effect the brake application.
2. Description of the Prior Art
Brake systems having a manually operated master cylinder and a power assisted hydraulic brake booster are not unusual for vehicles. Such systems have been used on trucks and an example of such a system is disclosed in U.S. Pat. No. 2,997,850. In this type system, the power assist is achieved through a pressure differential generated between vacuum generated at the intake manifold of the operating engine and air. While internal combination engines remain available for use in the trucking industry, it has been demonstrated that diesel engines are more economical. In order to use a vacuum brake booster with a diesel engine it is necessary to add a vacuum pump to the engine. As a result of the added cost, some vehicle manufactures have incorporated different brake systems in their trucks. In such systems, the size of the master cylinder and booster has utilized much of the space under the hood. Unfortunately in trucks commonly referred to a cab over design, this space is not available. In a cab over design, the cab is located over the engine and pivots to allow access to the engine. Presently remotely mounted boosters are typically actuated using a complex mechanical linkage connecting the brake pedal to the booster-master cylinder combination.